During the past decades there have been considerable developments within the field of radiation therapy and diagnostics. The performance of external beam radiation accelerators, brachytherapy and other specialized radiation equipment has improved rapidly. Developments taking place in the quality and adaptability of radiation beams have included new targets and filters, improved accelerators, increased flexibility in beam-shaping through new applicators, collimator and scanning systems and beam compensation techniques, and improved dosimetric and geometric treatment verification methods have been introduced.
Furthermore, a number of powerful 3-dimensional diagnostic techniques have been developed, ranging from computed tomography (CT), positron and single photon emission computed tomography (PET and SPECT) to ultrasound and magnetic resonance imaging, spectroscopy and spectroscopy imaging (MRI, MRS and MRSI). Equally important is the increased knowledge of the biological effect of fractionated uniform and non-uniform dose delivery to tumors and normal tissues and new assay techniques, including the determination of effective cell doubling times and individual tissue sensitives, allowing optimization of the dose delivery to tumors of complex shape and advanced stages.
Also new and improved designs of the constituent parts of a radiation therapy or diagnostic system, such as more stable and faster revolving gantries, have been developed. However, the body-supporting couches or tables of today, onto which a patient is positioned in a radiation therapy or diagnostic machine, are far from ideal, considering stability and user-friendliness issues.
FIG. 1 is a schematic illustration of a typical prior art body-supporting couch in a radiation therapy or diagnostic system. The couch is supported at one end by a couch support, situated at one side of a gantry of a radiation therapy or diagnostic machine. During treatment or diagnostic work up, a patient is positioned on the couch where a radiation source of the gantry irradiates a target volume in the patient. For radiation therapy, high-energy beams irradiate the target volume, typically including all tumor tissues to be eradicated. In diagnosing, diagnostic beams, most often with a lower photon energy, are incident on the patient and a dedicated detector, arranged in the gantry, captures radiation passing through the patient and provides anatomical information, typically an image of the irradiated target volume.
However, it is rather complicated for the patient to get onto a couch designed according to FIG. 1. This is basically a twofold problem. Firstly, since the couch is arranged extending through the gantry, the accessible free space of the couch is limited to its ends. The patient therefore, more or less, has to crawl into correct couch position starting from one end. Secondly, the smallest possible height of the couch is limited by the height of the opening through the gantry. In most gantry designs today, this height is about 70 cm or sometimes even higher, which is far too large for a comfortable getting onto/off the couch. In addition, once on the couch, medical personnel typically have to reposition the patient slightly to align with a predetermined position, e.g. according to a dose or treatment plan. The large height of the couch makes this procedure cumbersome and hard, possibly leading to strain injuries of the personnel.
In order to increase accessibility of the couch, a swingable patient couch or table may be used. In U.S. Pat. No. 5,014,292 an X-ray examination apparatus is described. The apparatus comprises a base assembly, including a pivotally and vertically displaceable frame, a first actuating means for pivotal movement of the frame about a horizontal axis and a second actuating means for vertical movement of the frame, two parallel rail systems supported by the frame and having two carriages mounted respectively thereon. One of the carriages supports a C- or U-shaped carriage for supporting an X-ray source and image receptor and the other carriage has an overhanging support secured thereto. This support in turn includes a dual action mechanism for supporting a patient table in an arrangement providing its vertical movement relative the frame and its pivoting movement about an axis parallel to its longitudinal axis.
The couch design described above may be rotated away from the gantry to facilitate getting onto/off the couch. However, since only one couch support, arranged at one end of the table top, is used (as for the couch in FIG. 1) once the patient is positioned on the couch it bends slightly due to the patient's weight. This bending depends on the actual position of the patient and is therefore complex to calculate in advance and compensate for. In radiation diagnoses and especially in radiation therapy, the actual position of the patient has to be accurately known to safely deliver the radiation dose correctly to the target volume. Any such significant bending of the couch makes a correct dose delivery very hard and in some applications practically impossible.
In U.S. Pat. No. 5,237,600 a height-adjustable patient support couch for use with an X-ray camera apparatus is disclosed. The couch includes a hydraulic multi-stage piston-cylinder, of which a top piston is driven in a vertical direction, a drive unit for driving the pistons in an axial direction and a multi-stage supporting device for supporting an overhanging load exerted by a patient on a couch or table top.
The patient support couch in U.S. Pat. No. 5,237,600 suffers from similar stability problem as U.S. Pat. No. 5,014,292 due to only one couch support, which was discussed above. In addition, if used with a radiation therapy or diagnostic machine with a circular gantry, the free accessible space of the couch is limited to its ends. This makes getting onto/off the couch very troublesome for the patient.